1. Field of the Invention
The invention relates to a method for testing a mass flow rate meter which functions according to the Coriolis principle, wherein an apparatus of the mass flow rate meter is subjected to a predetermined oscillation excitation and the associated oscillation response is recorded.
2. Description of Related Art
Coriolis mass flow rate meters generally have a measuring tube or a plurality of measuring tubes which, during operation, are excited into oscillation. A medium whose mass flow rate is to be determined and which flows through the measuring tube or tubes is thereby subjected to a Coriolis force, which leads to a change in the oscillation displacement relative to the oscillation excitation of the measuring tube or tubes. This change is used, for example, in the form of a phase difference in an oscillating measuring tube at sites spaced from each other for direct determination of the mass flow rate.
A difficulty with Coriolis mass flow rate meters is that, when they are used, over time, changes can occur which lead to a loss of measuring accuracy. In such a case, recalibration of the mass flow rate meter becomes necessary.
In order to rectify this problem, and in particular, to record a condition, which requires a recalibration of this type, it has been proposed in U.S. Pat. No. 6,092,409 that a method of the aforementioned type be used wherein a measuring tube of the Coriolis mass flow rate meter is excited into oscillation while a fluid flows through it, and through evaluation of the oscillations recorded, the density of the flowing medium is concluded. If the density of the flowing medium is known, by this means, the accuracy of the Coriolis mass flow rate meter during measuring operation can be determined. If appropriate, a warning signal may be issued, showing that the mass flow rate meter no longer measures sufficiently accurately and will have to be recalibrated or investigated regarding a possible error. However, a problem with this known method is that the density of the flowing medium must be known.